1. Field of the Invention
This invention relates to compositions and methods for controlling the growth of microorganisms and other contaminants in water processing systems, including, but not limited to, ice makers, water coolers, refrigerators, water filtration devices, cooling towers and water reservoirs. The compositions and methods of the present invention reduce the presence and/or inhibit the growth of microorganisms, such as fungi, algae, spores, molds, mildews, protozoa, bacteria and other contaminants of water processing systems. The composition contains a solid metal oxide which is at least partially immersed in a reservoir of the water recirculation system.
2. Description of the Related Art
Equipment used to process and store water often supports heavy growth of microbiological contaminants, such as bacteria, fungi, algae, spores, molds, mildews, and an assortment of other microorganisms. The presence of such contaminants in significant quantities is undesirable and creates unhealthy conditions in equipment used to process water for everyday use or consumption by humans, raising potential health code violations. Moreover, in equipment for processing non-potable water, such as cooling towers and water chillers used in cooling systems, overgrowth of contaminants can lead to fouling of process equipment, causing decreased efficiency and corrosion.
The site and identity of the contaminating growth may depend upon the particular chemistry of the water in the system, as well as upon the contents of the air near the water processing system. For instance, ice makers and water coolers located in bakeries, delis and other establishments having bread-making and other baking operations often suffer from heavy microbial growth covering up to 80% of the surface area of the equipment possibly due to the high quantities of airborne yeast in these environments which can get transported into the water processing system. It has also been noted that ice makers and water coolers located near copy machines tend to suffer from increased microbial growth. This is believed to be related to the presence of volatile organic substances used in the copying process and which are carried through the air to the water systems and provide nutrients the microbes.
Although attempts have been made to deal with the problem of overgrowth of such contaminants in water processing and holding systems, no successful remedy has been discovered. A traditional treatment for water contamination involves sterilizing the water with chemicals before it enters the processing equipment. This method has proven unsuccessful, because the contaminants generally grow on the surfaces of the equipment itself; thus, the sterilized water becomes contaminated again when it enters the process equipment. Cleaning the water prior to putting it into a contaminated system thus does not, significantly reduce the contamination of the water output. Additionally, the sterilized water does little to reduce the microbial build up already present in the system since the level of any antimicrobials in the water is generally not sufficient to reduce or destroy an established microbe infection in the equipment. The equipment can be disinfected prior to addition of the treated water; however, the cleaning process generally requires shutting down the system for long periods of time during the cleaning. Also, many contaminants are airborne and, as such, may enter the equipment after the pre-treated water has been added, and after cleaning has occurred.
Other prior art treatments include the use of chlorine as a disinfectant. Chlorination disinfects the water and equipment, but it also causes the equipment to corrode. In ice makers, the chlorine in the water becomes incorporated into the ice, giving an unpleasant taste and odor to the ice. Attempts have also been made, primarily in Japan, to decontaminate the water with magnesium pellets and ammonia. Although this method cleanses the water of contaminants, use of these chemicals in drinking water in the United States is not yet authorized by the EPA.
Ultra violet lamps have also been placed in or near the reservoirs of water systems to generate ozone, which poisons the microorganisms. However, this method also has not proven capable of efficiently reducing the growth of contaminants for a sustained period of, time. Additionally, this technique does not appear to work well at low temperatures, which makes it an impractical solution to microbial overgrowth in water coolers, refrigerators, ice makers, chillers, and other water processing equipment affected by this problem. Finally, this technique requires the consumption of additional electrical power.
A common problem with all of the above techniques is that while they achieve partial reduction of some microorganisms, they do not have a wide effectiveness; i.e. they typically cannot both reduce bacterial contamination and also control the growth of spores, fungus and algae for more than a short period of time.
Another prior art technique involves impregnating plastic with biocides and using the treated plastic to form the reservoir and/or other parts of water processing equipment that suffer from microbial growth. This method has proven relatively ineffective at reducing microbial growth to a sufficiently low level of detection. Making the impregnated plastic also involves increased costs associated with customized production of the parts for each different system or application. This method presents an additional problem in that the parts are not easy to obtain or replace. As with all of the above-described prior art disinfecting techniques, this method is only mildly successful in reducing the growth of microorganisms. Over a period of time, new growth of microorganisms will become sufficiently well established that the colonies of organisms will become visible to casual inspection of the surface of the equipment.
Thus, what is needed in the art are methods and compositions for quickly and effectively reducing or eliminating the growth of various microorganisms in water processing equipment and holding tanks and maintaining the reduced-microbial environment for sustained periods of time. Preferably, the method should also be convenient and cost-effective.
The invention relates to methods and compositions for reducing the growth of microorganisms and other contaminants of water processing and holding systems. As used herein the term xe2x80x9cmicroorganismsxe2x80x9d refers to any microscopic organism, including but not limited to algae, fungi, bacteria, protozoa, mold, mildew, and spores.
In its broad aspects, the invention relates to placing an antimicrobial material in any area of water processing, cooling or holding equipment where there is water movement or water storage. More particularly, the antimicrobial material is placed in a water reservoir or holding or overflow tank of such equipment. Placing the antimicrobial material in the water reservoir, where it is at least partially immersed in the water, destroys contaminating microorganisms in the water and on the surfaces of the equipment in contact with the water. Water-borne or air-borne microorganisms that subsequently contact the antimicrobial material are also killed. When placed in water processing equipment, such as an ice maker, water filtration device, or water recirculation apparatus, placing the antimicrobial material in the water reservoir reduces the presence of the contaminants in the entire system.
The invention provides methods and compositions for significantly reducing the growth of undesirable contaminants in water processing and holding equipment. The invention further provides methods and compositions which work quickly and require little expense or maintenance.
In a particular embodiment, the antimicrobial material of the invention comprises a powdered or fumed metal oxide. The metal oxide can be formed into a shaped solid, or into granules, pellets, extrudates, or other solid forms. The metal oxide may include, but is not limited to, oxides of titanium, silver, copper, zinc and zirconium, or combinations thereof.
In one embodiment, the antimicrobial material comprises at least titanium dioxide, especially fumed titanium dioxide. The titanium dioxide, whether fumed or granular or in some other form, may be optionally combined with other oxides, such as copper oxide, zinc oxide, or both.
The metal oxide or oxides may be blended with an additional material or substrate, typically an inorganic material such as alumina, silica, or carbon powder and with a binder, such as a high-density polyethylene binder. The metal oxide mixture may then be heated and compressed to form a solid shape, such as a block, for placement in a water reservoir.
Particularly in applications where the water in the reservoir is known or believed to contain quantities of H2S, the metal oxide material in the reservoir may be complemented by inclusion in the reservoir (at least partially immersed in the water) of a metallic composition comprising copper metal, zinc metal or an alloy of zinc or copper or both. The metallic composition may be added in the form of wires or a powder. In a particular embodiment the metallic composition is in the form of a wool of metal wire or filaments made from an alloy of zinc and copper.
The methods and compositions of the invention work quickly and efficiently, and have been demonstrated to reduce fungus, algae, spore, and bacterial buildup in ice machines by at least 99% within a few hours. The methods and compositions provided successfully reduce the growth of unwanted microbes and other contaminants in both hard and soft water and at a wide range of temperatures, from about 34xc2x0 to about 100xc2x0 F., for an unlimited period of time. In particular, the compositions and methods of the invention work very well at low temperatures in the range of about 34xc2x0 to about 38xc2x0 F. and particularly demonstrate excellent performance at temperatures of about 36xc2x0 to about 38xc2x0 F., which makes the invention particularly advantageous for use in water cooling equipment and ice makers.
Use of the methods and compositions of the invention in water coolers and ice makers in the restaurant business, which represents approximately 99% of the world-market for such. equipment, will reduce the exposure of consumers to microorganisms and other contaminants. This will significantly decrease a significant health risk as well as reduce the incidence of penalties and fees imposed by regulatory agencies.
These and further advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments.
The invention can be more clearly understood by referring to the following detailed description and specific examples. Although various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from reading this description, the description and examples are presented as illustrations and not intended to limit the scope of the invention in any way.
The invention rapidly reduces the growth of fungi, algae, spores, molds, bacteria, protozoa and/or other contaminating microorganisms in water processing and holding equipment. The method of reducing the unwanted microbial growth comprises placing a material comprising an antimicrobial composition in an area of such equipment where the water can contact and at least partially immerse the composition, e.g., areas where there is water movement or storage. As an example, the antimicrobial material may be placed in a water reservoir of the system. For instance, in an ice maker, the antimicrobial material can be placed in the area of the water reservoir near the water pump or other recirculation mechanism.
As discussed above, in one embodiment of the invention, the antimicrobial material contains a metal oxide. The presence of the metal oxide in the water is believed to result in a catalytic reaction which significantly reduces the growth of microorganisms. Appropriate metal oxides for use in the present invention include, but are not limited to, oxides of titanium, silver, copper, zinc and zirconium, or combinations thereof. In a particular embodiment, the antimicrobial material contains titanium dioxide, which may optionally be combined with copper oxide, zinc oxide, or both. While not wishing to be bound to any particular theory, it is believed that combining the titanium dioxide with zinc oxide and/or copper oxide provides enhanced antimicrobial activity because the titanium dioxide is particularly effective against bacterial contaminants, such as E. coli, while the zinc and copper oxides appear to be especially helpful in eliminating fungi and algae.
The metal oxide in the antimicrobial material of the invention may be powdered, granulated, or fumed. As used herein, xe2x80x9cfumedxe2x80x9d refers to particles ranging in size from about 20 nm to about 100 microns, more particularly from about 20 nm to about 25 microns, even more particularly from about 20 nm to about 100 nm. Fumed metal oxides have been found to be particularly suitable for this invention. In particular, fumed titanium dioxide, alone or combined with fumed copper oxide and/or fumed zinc oxide, has been found to work well. The granulated, fumed or powdered metal oxides may be formed into a compressed shape or block, granules, pellets, extrudate, or any other solid form capable of placement in a water reservoir. Alternatively the powdered or fumed metal oxides may be applied to or coated on a plastic shape, such as a honeycomb, capable of being at least partially immersed in the water in the reservoir. Such a shape should provide additional surface area for water to contact the metal oxide without significantly reducing the flow of water through the reservoir.
The metal oxide may optionally be combined with a substrate of alumina, silica or carbon powder. The metal oxide or metal oxide blended with alumina, silica or carbon powder may be additionally combined with a binder, such as high density polyethylene binder. For instance, an antimicrobial material of the present invention may comprise from about 2 to about 75 weight percent of metal oxide, from about 10 to about 25 weight percent of binder and from about 10 to about 70 weight percent of a substrate such as carbon powder, alumina silicate, or other silicate. The metal oxide portion of the material may contain titanium dioxide, or it may comprise from about 30% to about 90% of titanium dioxide and between about 10% and about 70% of copper oxide, zinc oxide or a combination of both. The portion of copper oxide and zinc oxide may contain these compounds in any ratio. Desirably, the copper oxide and zinc oxide are present in equal amounts (based on wt %).
In one embodiment approximately 22% wt of TiO2, 1.5 wt % of CuO, 1.5 wt % of ZnO was combined with 52 wt % of alumina, silica or carbon powder and blended with 23 wt % of a high density polyethylene binder. In another embodiment, 5% wt of TiO2, 2.5 wt % of CuO, 7.5 wt % of ZnO was combined with 65 wt % of alumina, silica or carbon powder and blended with 20 wt % of a high density polyethylene binder. The compositions of the invention can be formed into a porous block by mixing and heating in a mold until the binder becomes flowable. This block can then be simply introduced into, e.g., the water reservoir of an ice maker, where it will operate to keep the surfaces of the icemaker virtually free from microbial growth.
For example, the compositions described above may be heated to high temperatures, from approximately 280xc2x0 to approximately 65xc2x0, preferably from about 350xc2x0 to about 400xc2x0 F., for approximately 1.5 to 3 hours to melt the binder, followed by compression and cooling to form a hydrophilic solid material with a strong surface attraction for microorganisms, such as the porous block described above.
In one embodiment the metal oxide composition is heated to extremely high temperatures, from about 700xc2x0 to about 1100xc2x0 C., sufficient to cause the binder to decompose, resulting in a porous, more hydrophilic solid, which provides increased surface area for the contaminants in the water to contact the metal oxide.
The composition may also be formed into pellets or granules, e.g., by extruding the mixture and chopping or grading the extrudate.
In yet another embodiment, the metal oxide composition may be combined with a metallic material comprising copper metal, zinc metal or an alloy of zinc or copper or both. The metallic composition may be in any form. Wires or powders have been found to be suitable. In a particular embodiment, a metallic wire made out of an alloy of zinc and copper is used. The metal wire can be in the form of a metal xe2x80x9cwoolxe2x80x9d that can be at least partially immersed in the water of the reservoir to be treated. In a particular embodiment, the metal oxide is titanium dioxide, and a metal wool is used that contains zinc and copper, in a zinc to copper ratio ranging between about 70:30 and about 50:50. The combination of the metal oxide with the metal wool significantly reduces the concentration of bacteria, mold and yeast in water systems and is particularly useful when the water contains hydrogen sulfide. This is believed to result from redox reactions which occur in the presence of hydrogen sulfide.
The metal oxide compositions described above successfully reduce the growth of unwanted microbes and other contaminants in both hard and soft water and at a wide range of pH levels and temperatures for significant periods of time. The compositions and methods of the invention exhibit maximum efficiency at a pH range between about 5.5 and about 8.5. The invention effectively reduces microbial growth at temperatures from about 34xc2x0 to about 100xc2x0 F., more particularly from about 34xc2x0 to about 85xc2x0 F. These compositions and methods also work very well at low temperatures in the range of about 34xc2x0 to about 38xc2x0 F. and particularly demonstrate excellent performance at temperatures of about 36xc2x0 to about 38xc2x0 F., a significant advantage for disinfecting water cooling equipment and ice makers.
The antimicrobial material of the present invention is used in such amounts as necessary to effectively reduce the level of microbial growth in the water system. The surface area of the material may represent between 2 and 10% of the total surface area of the reservoir of the system, but this range is not meant to be limiting and much smaller or larger amounts may be employed as necessary for each particular system. A particular advantage of the present invention is that very small amounts of the antimicrobial material may be effective at virtually eliminating all contaminating growth within a matter of hours, as is demonstrated in the examples below. For instance, the metal oxide may be present in amounts ranging from about 2% to about 75%, more particularly from about 14% to about 30%.